A recent trend of a removable storage medium such as a Universal Serial Bus (shortened as USB hereafter) memory is that technology for erasing stored data upon the medium being connected to a Personal Computer (shortened as PC hereafter) is employed so as to prevent information leakage in case of loss or theft of the medium. Such kind of USB memory technology includes information of what activates a data erasing program in the USB memory in case of connection with a PC and automatically erases temporarily accessible data (e.g., refer to Japanese Laid-open Patent Publication No. 2006-195629). Further, it includes information of what deletes a file which has expired by means of a data erasing program (e.g., refer to Japanese Laid-open Patent Publication No. 2008-140127).